This invention relates to seismic exploration methods for determining the location and course of subsurface earth structures.
A common method of seismic exploration is carried out by locating a string of spaced seismic detectors along a straight line at the surface of the earth. A seismic source is located in line with the detectors and operated to produce a seismic disturbance. Such disturbance produces subsurface reflections which are received by the detectors and recorded for later analysis. The string of detectors is then picked up and relocated either along a second line running parallel to the first line or at a new location in line with the first line and the foregoing process repeated for the second location. This process is continued until the desired area has been surveyed. As is apparent, this process can become rather tedious and time consuming where a relatively large surface area of the earth is to be surveyed.
A known problem which exists in the seismic exploration art is that of distinguishing the desired subsurface earth structure reflection signals from various extraneous seismic vibrations which are also received by the detectors and which are commonly referred to as "noise". A known technique for minimizing such noise is commonly referred to as "stacking". Such stacking technique involves the use of multiple sources for obtaining multiple reflections from a common subsurface point. After appropriate processing, the individual recordings for the common subsurface point are combined to produce a composite record wherein the desired signal components are emphasized and the undesired noise components are minimized. This stacking technique is described in greater detail in U.S. Pat. No. 2,732,906, granted to W. H. Mayne on Jan. 31, 1956 and in U.S. Pat. No. 3,040,833, granted to H. L. Mendenhall and S. D. Elliott on June 26, 1962.
It is an object of the present invention to provide new and improved methods of seismic exploration for obtaining a greater amount of data concerning subsurface earth structures for a given expenditure of time and labor or conversely, for obtaining a given amount of data for a lesser expenditure of time and labor.
It is another object of the invention to provide new and improved seismic exploration methods for enabling a greater degree of stacking for a given expenditure of time and labor.
It is a further object of the invention to provide new and improved seismic exploration methods for obtaining better data concerning subsurface earth structures.
Another object of the invention is to provide seismic exploration methods capable of penetrating seismic diffraction barriers created by objects in, in the neighborhood of, or above a geologic region of interest.
Yet another object of the invention is to provide methods for seismically exploring a geologic region of interest so located with respect to a surface feature, such as an inhabited area, or a subsurface feature, such as a salt pocket above the region, that substantially no meaningful seismic data can be obtained by running a survey line across the feature and the geologic region of interest.
For a better understanding of the present invention, together with other and further objects and features thereof, reference is had to the following description taken in connection with the accompanying drawings, the scope of the invention being pointed out in the appended claims.